The primary functions of a drilling fluid or mud are: to carry chips and cuttings produced by drilling to the surface; to lubricate and cool the drill bit and drill string; to form a filter cake which obstructs filtrate invasion in the formation; to maintain the walls of the borehole; to control formation pressures and prevent lost returns; to suspend cuttings during rig shutdowns; and to protect the formation for later successful completion and production. Friction between the drilling apparatus and the borehole is a problem. The greater the friction, the higher the energy required for the drilling process. The higher the friction, the more likely other problems such as drill bit sticking are to occur. In addition, in non-vertically, e.g. horizontally, drilled wells, a reduction in the coefficient of friction makes the non-vertical drilling operation easier. Accordingly it is desirable to use a friction modifying agent which decreases the friction of the drilling process and thereby decreases the probability of bit sticking, decreases the energy costs of drilling, and facilitates non-vertical drilling. It is an object of this invention to supply such a friction modifying agent.
Useful drilling fluids or muds must maintain rheological and viscosity properties under normal operation conditions. Also, the drilling fluids or muds must be able to suspend cuttings and weighting materials upon stopping of circulation of the drilling fluid. It is desirable to have drilling fluids or muds which maintain thixotropy and rheology even with increased solids. Weighting agents and organophilic clays may be used to provide higher viscosity and density to the muds.
There are two major types of drilling fluids, or muds, in use today. In addition, a somewhat different foam drilling fluid is occasionally used. The fluids are either oil based or water based. The oil based fluids are generally water-in-oil emulsions which contain some water in the form of a discontinuous emulsified phase. The oil is the continuous phase. The other major type of drilling fluids are the water based drilling fluids These water based compositions may contain some oil phase. If oil is present, it exists as a discontinuous emulsified phase. Accordingly, the water based fluids which contain oil, are oil-in-water emulsions. Since the external properties of emulsions, such as dispersability, wetting characteristics, and feel, are determined by the continuous phase, the oil based fluids are more like oil, even though they contain water, and the water based fluids are more like water, even though they may contain oil.
The drilling muds of the present invention are water-in-oil emulsions. The optional weighting agents and organophilic clays are generally in the oil phase of the muds. If these materials become water wet (e.g. present in the brine phase of the emulsion), then the emulsion is weakened. If the emulsion is weakened sufficiently, the emulsion may flip, e.g. go from an water-in-oil (e.g. invert) emulsion to a oil-in-water (regular) emulsion. When the emulsion flips, it renders it unusable in well-drilling applications.
U.S. Pat. No. 3,236,769 discloses drilling fluids containing water and clay to which is added a defoamant and a water-soluble, non-ionic compound having surface active properties and characterized by the formula: R-(x-[(CH2-CH2-0)n-H]m)y. The non-ionic compound functions as a flocculating or agglomerating agent for clay.
U.S. Pat. No. 4,031,023 discloses lubricating compositions having oxidative stability and anti-wear properties contributed by certain hydroxy thioethers. These thioethers include molecules such as 2-hydroxy ethyl n-decyl sulfide.
U.S. Pat. No. 4,172,800 discloses aqueous drilling fluids containing an admixture of a polyethoxylated sulfurized fatty acid and polyalkylene glycol. Such fluids are especially useful where reduced torque drilling fluids are needed.
U.S. Pat. No. 4,181,617 discloses an aqueous drilling fluid having a lubricant consisting essentially of the reaction product of a fatty vegetable oil with 4,4'-thiodiphenol.